High frequency electron tube device



Feb. 9, 1960 v v H. o. G. ALFVEN 2,924,741

HIGH FREQUENCY ELECTRON TUBE DEVICE if $3 Filed Nov. 25, 1955 4 Sheets-Sheet 1 1 Hmvmzs Oz 0: 605; 9. Haw

Hm M NM firromvsrs Feb. 9, 1960 H. o. s. ALFVEN HIGH FREQUENCY ELECTRON TUBE DEVICE Filed Nov. 25, 1955 4 Sheets-Sheet 2 O Q I 17v rs/v 70R I VEN Hnmvss 0101-5663277 flu Feb. 9, 1960 H. o. G. ALFVEN' 2,924,741

7 HIGH FREQUENCY ELECTRON TUBE DEVICE Fiied Nov. 25, 1955 I 4 Sheets-Sheet s [NI/ENTOR I Ham/v55 040/- 603779 194 FVIV Feb. 9, 1960 HQQ. G. ALFVEN 2,924,741

EEEEEEEEEEEEEEEEEEEEEEEEEEEEE CE nited S This. inventionrelates to electron tubes for generating and, amplifying high frequency electron oscillations.

Generally electron tubes, inwhich electrons are: caused tooscillate, are usedfor generating highjrequency oscil-.

lations. In: the hitherto; known devices of thiskindthe electron oscillations, are generated by means of. electric fields whichsometimes are combined. with magnetic fields as-in. themagnetrons and the so-called strophotrons. In electron tubes utilizing combined electric and magnetic fields the magnetic field may be made inhomogeneousforthe. purpose of efiecting a continuous drift motion ofthe electrons in av certain direction rather to produce oscil lations of the electrons.

In an electron tube device according to the invention the electrons, are by means. of an electron gun injected. into a discharge spacehaving no static electric fields and theoscillations, of the electrons are obtained exclusively by means, of aninhomogeneous magnetic field. In this way a maximum efficiency isobtained as the electrons can deliver a. high percentage of their energy to ahigh frequency, circuit coupled; to the electron beam without simultaneously taking upenergy from. a D.-C. electric .An electron tube device according to the inventioncom prises a source for emitting electrons which are subjected to a drift motion along a discharge space simultaneously. with an oscillatory motion perpendicularly to the median path of the drift motion, electrode means for setting up analternating electric field exchanging energy with the oscillating electrons, and acollector electrode. The drift and the oscillatory motion of theelectrons are caused by a non-homogeneous magnetic field. This field has in the projection upon a, plane perpendicular of the median path of the drift motion in which the electrons move, a maximum value on either side of the median path andextends in opposite directions on either side of said average path.

The invention will be described more in detail in connection with the accompanying drawings.

Fig. l is a diagrammatic plan view ofthe electrode system in an electron tube according to the invention.

Fig. 2 is an end view seen in the direction of the yaxis of the electrode system according to Fig. 1.

Fig. 3 is a graph. showing the required distribution of the magnetic field seen in a plane perpendicular to they-axis in Fig. 1

Fig. 4 is a diagram of a modified electron path in an. electron tube according to Fig. 1.

Fig. 5 is a cross-section taken on line 5-.5 of Fig. 6 and shows atube, according to the invention disclosing one arrangement for generating the magnetic field.

Fig. 6 is alongitudinalsection taken on line 6-6 of atented Feb, 9, 1960 Fig. 9 is a longitudinal section taken, on line 9--9 of Fig. 8.

Fig. 10 is an isometric view of an amplifier system according to the invention.

Fig. 11 is a longitudinal section taken on line 11 1 1, of Fig. 12 and showing a further embodiment of an electron tube device according to the invention. 7

Fig. 12 is a cross-section taken on line 1212 of'Fig. l1, and

Fig. 13 shows a further graph of'anelectron path.

In Fig. 1 showing the principle of an electron tube device according to the invention an electron gun of conventional design is designated by 2, said electron gun being arranged to generate a narrow or concentrated electron beam wnich is directed into theregion or zone desig; nated by I. This space is transverse by a perpendicular magnetic field B which is directed towards the plane of the paper. magnetic field, the field 'lines of which are also directed perpendicular of the plane of the paper but upwards. Between the regions land ll thereis a region or zone I II substantially free of the field. Two electrodes. 3 and 4 are connectedto a resonance circuit 5.

Let it be assumed that nohigh frequency field is, applied to the electrodes 3 and 4, then the electron beam will be deviatedto the right when it is entering the magnetic field region I at a, and if the velocity of the electron bearn and the strength of the magnetic field are properly selected the electron beam will leave said. magnetic field region at;

b and pass into the field freeregion Ill, The electron:

beam is then entering tne magnetic field of the region II' where it isdeviated to the left in such a way that it again entering thefield'free region. In this way the electron beam is performing a continuous motion along a mean path and an oscillatory motionperpendicularly,to said mean path.

The electron tube device is operatingas generator, for example in the following manner. The high frequency. circuit 5 is tuned in such a way, that the resonant fre quency is equal to the period of'oscillation of t e electrons or to some of'its odd multiples or suhmultiples; A necessary. condition for anenergy exchangebetween the electron beam and the high frequency field between the electrodes 3 and' 4. emanating from the tuned circuit is, as in other tubes in which the generation of oscillations is obtained by means of oscillating electrons, that the electron beam is intensity modulated. The beam can be intensity modulated already in the electron gun before entering the magnetic field. The electron beam can also be automatically1 intensity modulated as a continuous electron beam entering a magnetic field already is automatically phase focused after a few oscillations so that intensity maxima and minima are formed in the beam. This focusing has been found to be very stable which contributes to the good efliciency of the'device. When the electrons have given up the main part of their energy they are suitably collected by a collector electrode 7 for preventingdisturbing space discharges in the tube.

The electrons may deviate a certain distance upwards or downwards from the plane of the paper, but if they deviate too much from this plane they must be returned to the vicinity of this plane. This can be accomplished, for example by means of giving the magnetic field'a falling characteristic at the apsides of the electrons, seen in a plane perpendicular to the mean path of the drift motion. This is illustrated in Fig. 3; which shows adiagram-of the magnetic flux density B as a function of the distance from said mean path. As is seen from thisidiagram the flu density must be zero in the mean path and have maxima.

Another region orlzone II is traversed by a.

The electron beam can also be stabilized by means of an electrostatic field which returns the electrons to the vicinity of the plane of oscillation. I i

If the magnetic field is shaped as shown in Fig. 3 the electron path will be more complicated than that shown in Fig. 1 and an example of such a path is shown in Fig. 4. The character of the path "can easily be changed by adjusting the angle at which the electron beam is directed into the inhomogeneous magnetic field. As the distance travelled by the electrons during a period of oscillation is varying with the angle at which the electron beam enters the magnetic field it is obviously very easy to change or modulate the frequency of the electron oscillations simply by varying the angle of entry by means of an electrostatic or magnetic deflection system located in or adjacent to the electron gun.

Figs. 5 and 6 show an electron tube comprising an evacuated envelope 10 in which four magnetic pole shoes 11, 12, 13, 14 which are so located that the vertical component of the magnetic field has the same distribu tion along a horizontal diameter as is shown in Fig. 3. The pole shoes are magnetized by means of externalmagnets 15 and 16 in such a way that the pole shoes 11 and 14 become north poles and the pole shoes 12 and 13 become south poles. Twoelectrodes 17 and 18 are located within the tube envelope and connected to a tuned circuit in the same manner as shown in Fig. l. Acollector electrode 19 is arranged for collecting the electrons. In Fig. 6, there is shown an electron gun 20 and a system 21, 22 of deflection electrodes, by meansof which the angle can on entry of the beam be varied. The electrons are suitably iniected into the envelope in such a 'way that they will oscillate along the horizontal diameter along which the resulting field strength is zero.

Fig. 7 shows a section perpendicular of the drift or longitudinal direction, that is of the y-axis as defined in Fig. l, of an electron tube similar to that .shown in Figs. 5 and 6 except for the magnet arrangement. According to Fig. 7, the non-homogeneous magnetic field is generated by only two pole shoes 23, 24. Owing to the horizontal component of the magnetic field, which appears in this arrangement, the electrons will also oscillate in a vertical direction in a more or less pronounced trochoidal path. The oscillation energy can for example be taken out between the electrodes 17 and 18 or between these electrodes interconnected and the magnet. In the latter case the oscillation frequency is preferably equal to twice the frequency of the electrons.

Figs. 8 and 9 show a further embodiment of the invention, where the magnet poles within the tube are replaced by conductors passed by current. In this figure 27 and 28 designate two elongated coils passed by a current flow which conductors are so located, that adjacent parts of the two coils are passed by currents having the same direction. The electron beam of the electron gun 2 is injected substantially in the symmetry plane of the two coils, and the electrons will oscillate in a surface in the space between the coils. The magnetic field may be shaped in such a way that the field strength increases or decreases along the direction of the translational motion or in such a way that the gradient is varying along the path of the translational motion. ,In this, way it is possible to vary the period of the electron oscillations or to keep it constant although the amplitude is changed. Thus it is possible to keep the oscillation frequency constant in spite of the decrease of the amplitude which is obtained along the direction of the translational motion when the tuned circuit is-loaded. This arrangement will give the device maximum efiic ency. a

, Fig. 10 shows schematically the electrode arrangement of an amplifier tube according to the invention. This tube is built up principally in the same way as shown in Fig. 7. The electron gun and the collector electrode are for the 4 4 sake of simplicity deleted in the figure, but they may be arranged in the same way as shown in Fig. 6. The electrodes 17 and 18 of Fig. ti are in Fig. 10 divided into three groups 30, 31, 32, 32' and 33, 34. The electrodes 30, 31 form an input section and they are connected to the source 36 of the voltage to be amplified. The intermediate electrodes 32, 32' are directly interconnected and form a screening section between the input section and the third sectiond formed by the electrodes 33, 34, which serves as output section and is connected to a load 37.

Electrons emitted from the electron gun will, if no signal is impressed on the input section 30, 31, oscillate with is sustained during the screening section 32 and at the entry into the output section the electron bunches will induce an amplified signal in the electrode system 33, 34 of the output circuit, which signal is taken out to the load 37. V

Figs. 11 and 12 show two sections. of an electron tube device where the electrode system and themagnetic pole shoes together form a resonator. The evacuated envelope 38 consists of an elongated cylindric metallic housing provided with two inner wedge-shaped projections projecting into the space between the pole shoes 11 and .13 and between 12 and 14, respectively. The spaces 39 formed between the pole shoes 11 and 12, and between the pole shoes 13 and 14, respectively, together with the space 41 between the radiallyinner endsof the wedge-shaped A projections form the resonant chamber which is tuned to the desired oscillation frequency.

resonant chamber having low losses the inner walls In order to obtain a of the resonant chamber, i.e. the surfaces of the magnetic pole shoes 11, 12, 13, 14 and the parts of the metallic envelope limiting said chamber are plated with a suitable low. loss metal suitable for use in vacuum, for

example gold. The electron beamen anates from the electron gun 20, which is only schematically shown but this gun can be of any convenient kind known in the prior art. The electrons are oscillating horizontally in the space 41 in the electric field of the high frequency electromagnetic field of the resonator which electric field is concentrated to the space 41. The frequency of the electron oscillations may be varied or modulated by means of changing the angle of the entry of the electron beam,

the velocity of the electron beam or the strength, of the magnetic field in analogy with the earlier described embodiments. The high frequency energy is taken out by means of an inductive loop 42 projecting into the cavity 39 of the resonator. The electrons, which have passed the discharge space and given up their energy to the high frequency field, are as in the other embodiments caught by a collector electrode 19. The magnetic flux to the pole shoes 11, 12, 13 and 14 is as before described supplied by external magnets 15 and 16, so that the pole shoes 11 and 14 become north poles and the pole shoes 12 and 13 become south-poles. i

Fig. 13 shows a further typeof electron paths possible inan electron device according to the invention. In this case the magnetic field is somewhat stronger than in the above embodimerltawhereby the radius of curvature is smaller. It is to be observed that themagnetic fields within the regions I and II, respectively, have directions opposite to those shown in Fig. 4. If the directions of the fields were the same as in Fig.4 the electrons would obviously move backwards, i. e. to the left in the figure.

Qf courseit .isv possible to modify the invention in a plurality of dilferent ways. For example the inhomogeneous magnetic field may be generated in different ways, and the shape and arrangement of the electrodes may vary.

I claim:

1. An electron tube device for generating high frequency electron oscillations, comprising an evacuated elongated envelope having a longitudinal extending plane of symmetry, electron reflecting electrode means disposed in said envelope symmetrically of said plane, terminal bias means for applying to said electrode means a substantially equal bias potential, said electrode means defining within the envelope a longitudinally extending discharge space substantially free of electrostatic fields, a source of electrons generating a concentrated electron beam directed into said discharge space at one end thereof, the electrons in said beam being contained in an oscillation plane perpendicular of said plane of symmetry and parallel to the longitudinal direction of said discharge space, electron collecting electrode means at the other end of said discharge space, and means for generating a magnetic field in said discharge space, said field having at least a major component perpendicular of said oscillation plane, said major component having a zero value in said symmetry plane and opposite directions on opposite sides of said symmetry plane, the magnetic field having at least one maximum of different polarity on each of said opposite sides of the symmetry plane whereby the electrons are caused to oscillate substantially in said oscillation plane between the reflecting electrode means While progressing along the discharge space.

2. An electron tube device for generating high frequency electron oscillations, comprising an evacuated elongated envelope having a longitudinal extending plane of symmetry, electron reflecting electrode means disposed in said envelope symmetrically of said plane, terminal means for applying to said electrode means a substantially equal bias potential, said electrode means defining within the envelope a longitudinally extending discharge space substantially free of electrostatic fields, a source of electrons generating a concentrated electron beam directed into said discharge space at one end thereof, electron collecting electrode means disposed at the other end of said discharge space, and means for generating a magnetic field having at least one major component directed perpendicular of said plane of symmetry, said major component having a zero value in said plane of symmetry and maxima of different polarities on opposite sides of said lane of symmetry whereby the electrons in said beam are caused to travel along a path oscillating about said plane of symmetry and progressing along the discharge space toward said collector electrode means.

3. Electron tube device according to claim 2, characterized in that the output energy of the electrons and the strength of magnetic field are such that the turnover points of the electrons in the oscillation path are located at a greater distance from said plane than said field strength maxima.

4. Electron tube device as claimed in claim 2, characterized by means for varying the angle of entry of said beam into said envelope.

5. Electron tube device as claimed in claim 2, characterized therein, that the strength of the magnetic field is varying in such a Way that the oscillation frequency is,

constant along the discharge space in spite of the decreasing energy of the oscillating electrons along said space.

. 6. Electron tube device as claimed in claim 2, comprising magnetic pole shoes projecting into the discharge space, characterized therein, that said pole shoes and parts of the envelope form a resonator in which the electrons oscillate and interchange energy with the electric field within said resonator.

7. An electron tube device according to claim 2, wherein said means for generating the magnetic field comprise tWo magnets having pole pieces protruding into said discharge space and extending longitudinally therein, like poles of said magnets facing each other in diametrical arrangement across said plane of symmetry.

8. An electron tube device according to claim 2, wherein said means for generating the magnetic field comprise a magnet having pole pieces disposed within the envelope in a position in which the magnetic field has a component parallel of said plane of symmetry, said parallel component causing the electrons to oscillate in perpendicular direction along a generally trochoidal path.

9. An electron tube device according to claim 2, wherein said means for generating the magnetic field comprise coiled conductors extending Within said envelope in generally longitudinal direction, adjacent parts of said conductors being disposed to be traversed by a flow of current in the same direction.

10. An electron tube device according to claim 2 for amplifying a voltage, wherein said reflecting electrode means comprise three pairs of electrodes disposed in longitudinal alignment within the envelope, the pair next adjacent to said source of electrons constituting the input section adapted to be connected to a voltage to be amplified, the electrodes of the intermediate pair being interconnected and constituting a screening section, and the electrodes of the third pair constituting the output section adapted to be connected to a load.

11. An electron tube device according to claim 2, wherein said means for generating the magnetic field comprise two pairs of magnets having pole pieces extending into the envelope, like poles facing each other in dithe resonance chamber in conjunction with said polepieces.

References Cited in the file of this patent UNITED STATES PATENTS 1,985,093 Hehlgans Dec. 18, 1934 2,414,121 Pierce Jan. 14, 1947 2,513,260 Alfven et al. June 27, 1950 2,761,088 Warnecke et a1 Aug. 28, 1956 FOREIGN PATENTS 729,930 Great Britain May 11, 1955 

